Vibratory machines have been well known for many years for a large number of different uses, including screening of cohesive powder and sticky materials, compacting of concrete mixtures and powders, tamping of soil and asphalt, shaking-out of molds and casting, crushing, milling and mixing power of powders, deburring and finishing of casting with intricate shaping, and bin activation. Such machines further find application in a plurality of fields, including the construction industry, manufacture of building materials, processing of raw materials, mining, metallurgy, mechanical engineering, foundry associated applications, manufacture of ceramics and powders, the food industry, pharmaceuticals and chemicals.
Numerous different types of unbalanced vibrator units employing rotating shafts and eccentrically fixed weights, are utilized to drive these vibratory machines and devices. In particular, it is common to find unbalanced vibration motors or vibrators with external drive motors, used to drive different vibratory machines, which are supported on "soft" elastic mounts. The natural frequencies of these over-tuned machines are essentially less than the forced frequency of the vibrator units driving them, and such vibration units do not require adjustment or tuning. These vibrator units are supplied on the market as "ready-made" replaceable assemblies, such that use and service of such units are simple, relatively cheap and convenient.
It is known, however, that the required excitation forces in over-tuned machines must be large, causing great bearing losses and a waste of energy. Another disadvantage for many applications is the fact that they require multifrequency waveforms, rather than the single-frequency sine waveforms generated by an unbalanced vibrator. These applications include vibrator compacting, crystallization, screening, grinding, mixing, and so on, and require a member of harmonics with different frequencies and amplitudes, such as disclosed in U.S. Pat. No. 4,891,190 to Carter and U.S. Pat. No. 4,859,070 to Musschoot.
Also known are vibratory machines in which an unbalanced vibrator unit has an additional weight which is connected to a vibratory device by means of elastic constraints, thereby to provide tuned vibration and to increase the amplitude of the vibratory device under a non-varying single-frequency excitation force. One known form of an unbalanced vibrator unit of this type is used in the "Carriage Mounted Vibrating Charge Feeder," which is shown on page 7 of the Bulletin No. 580-A of the General Kinematics Corporation, entitled "Vibrator process equipment for the cost efficient foundry", published in 1992. These tuned machines undoubtedly save energy when compared with similar, non-tuned machines. However, machine working modes can be sensitive to loading such that, if the working load changes a tuning adjustment may be required. A further disadvantage of these machines is the provision of a single frequency motion of the working unit, which is inherently non-optimal, as discussed above.
There is also known a vibratory machine of another type, which employs a working unit supported by elastic mounts, an impact member with a fixedly attached unbalanced vibrator, and a plurality of elastic shear elements an buffers provided between the impact member and working unit. A harmonic force of the unbalanced vibrator excites the impact member and, due to repeated collisions of the impact member with the elastic buffers, the harmonic force is transformed into a multi-frequency force. This multi-frequency force is conducted to the working unit of the vibratory machine.
A vibrator unit of this type is described in conjunction with a vibration-impact table for mold compaction of concrete mix in USSR Patent No. 1821370. A multifrequency vibration machine of this type has a number of advantages, including the provision of an optimal waveform, high work efficiency and energy saving in comparison to over-tuned machines. The present inventors have found that the use of multi-frequency machines such as described in the above-reference USSR patent facilitates a 75% reduction in the required power input to the drive. A machine of this type, furthermore, costs about half of the cost of an over-tuned machine as described above.
This type of machine is characterized, however, by a temperature instability of the elastic shear elements associated with the impact member, which can lead to a failure, both of these elements and of the machine as a whole. Another shortcoming is the rapid irregular wear of the buffers' surfaces as the result of elliptic trajectories of the impact member relative to the working unit, and resulting skewed impacting of the buffers' surfaces. Both of these disadvantages result in necessary frequent adjustment or tuning of the machine by skilled personnel. Turning in industrial conditions is very labor-consuming and requires special equipment.
Impact vibrator units, which contain electromagnetic vibrators and special adapters, are shown in an article entitled "Vibrations and Schweisstechnik", published by the AEG Actiengesellchaft Company. Such vibrator units are intended for impact activation of the wall of a bin by means of directly acting electromagnetic vibrators. An adapter, provided as a separate unit, includes rubber elements and an impact bolt, which are operative to transfer vibrational forces and unilateral impact impulses to the bin wall, thereby activate bulk material flow.
Disadvantages of this vibrator drive unit include its low power of less than 0.5 kW, and an absence of a force component normal to the impact direction. Both disadvantages are inherent in electromagnetic excitation.